The present disclosure is directed generally to an apparatus and method for manufacturing a semiconductor device, and specifically to reducing sodium concentration in a transparent conductive electrode of a semiconductor device.
A “thin-film” photovoltaic material refers to a polycrystalline or amorphous photovoltaic material that is deposited as a layer on a substrate that provides structural support. The thin-film photovoltaic materials are distinguished from single crystalline semiconductor materials that have a higher manufacturing cost. Some of the thin-film photovoltaic materials that provide high conversion efficiency include chalcogen-containing compound semiconductor material, such as copper indium gallium selenide (CIGS).
Thin-film photovoltaic cells (also known as solar cells) may be manufactured using a roll-to-roll coating system based on sputtering, evaporation, or chemical vapor deposition (CVD) techniques. A thin foil substrate, such as a foil web substrate, is fed from a roll in a linear belt-like fashion through the series of individual vacuum chambers or a single divided vacuum chamber where it receives the required layers to form the thin-film photovoltaic cells. In such a system, a foil having a finite length may be supplied on a roll. The end of a new roll may be coupled to the end of a previous roll to provide a continuously fed foil layer.
Sodium enhances the electronic properties of some chalcogen-containing compound semiconductor materials (such as CIGS) by reducing density of defects, increasing net carrier concentration, and electrical conductivity, thereby improving the conversion efficiency of a photovoltaic device employing the chalcogen-containing compound semiconductor material. It is believed that sodium achieves such electronic effects through structural modification of the chalcogen-containing compound semiconductor material, which includes increased grain size and texture due to the presence of sodium during growth of the chalcogen-containing compound semiconductor material.